Your love of audio, and devotion to rolling your own is a boon to us all. I’ve been an avid DIY audio geek (now professional – but I still roll my own and geek out at home regularly) for ~~ 3 decades now. Having heard the dynamics and low distortion available from Line Array’s – I’ve always wanted to try them in a home theater environment.
My issue had always been two things. 1 – I’m looking for constant directivity over as large a frequency spectrum as I can attain (my holy grail). 2 - the inability to also use a line array for the center channel on its side.
I require my front three speakers to be as close to identical as possible with the same voicing, a straight non shaded line array just doesn’t have the lateral coverage necessary, lobes and combe filters too much – and won’t center the image on the screen’s center..
Your CBT Center is my answer!! I am so glad Don convinced you to give it a try! Thank you for the incredible level of work you’ve gone through in documenting it for us (well that and the actual build
. I am extremely excited to start heading down the CBT path myself… Eventually I would like to build a pair of G.P. CBT’s for L/R duty, several smaller variants for surrounds, and a full CBT for the center..
I am especially happy to hear the legendre shading keeps vocals centered roughly in the middle of the screen as you move off axis. This has been my biggest sticking point – the desire to use a solid screen and maintain a fixed center image directly in the center of the screen.
On a side note – regarding your comment about your reticence to try G.P. CBT’s verses full height CBT’s above for L/R duty – you may have the answer to your fears sitting in your HT already:
After careful review of the measurements Don posted for CBT’s and ground plane CBT’s – I suspect that a half height ground plane CBT would be Ideal
as replacements to your current straight line arrays..
Since you’ve already got the straight line array enclosures built repleat with HANN shading– It might be useful to digitally delay the signals and see how they sound. IOW, use digital delay and legandre shading to generate the equivalent of a full CBT, as described in don’s papers.
This way you will have a strong idea of the potential improvement in SQ going from straight to CBT array for your L/R’s.. You could also test whether you would prefer full height CBT’s or ground plane CBT’s all on the same straight L/R line arrays you currently run before ever cutting wood..
After calculating all the potential listening heights angles (which I suspect you already know ) – choose a ground plane CBT curvature and height that properly covers the entire intended listening area, and truncate the line electronically. Only use those speakers needed. You could use delay and shading to approximate different curvatures even.. You could then invert this effect and evaluate a ceiling verses floor mounted G.P. CBT
If you do entertain the idea of testing this – once you build what you’ve decided on, to address the harshness issue of your current L/R’s in the top octave, I recommend incorporating the tweeters used in your center for your new L/R CBT’s or G.P. CBT’s.... The majority of the answer lies in your post #5 under this thread:
Originally Posted by Montekay
I have proven to myself, forgotten or disbelieved myself and then proven to myself again that driver resonance peaks must be removed even if they are well beyond the frequency band where the driver is to be used. If you don't do this, the speaker will sound harsh. The strange thing is that this is true even if there is no visible effect to the total system frequency response measurement. That's why I always disbelieve myself and end up having to prove it to myself again.
Those Aura’s have a breakup mode above 10K that can be heard, and I suspect this is the majority of the harshness you currently experience with your L/R’s relative to your center even after shading..
I gotta say – at some point I would love to head down to Austin and give your system a listen!!